1. Field of the Invention
The present invention relates to a novel oil and fat composition and to methods for using it to lubricate machines and tools for agriculture and food processing and like machines and tools. More particularly, the present invention relates to a novel oil and fat composition for food processing machines which is safe for food sanitation, has excellent lubricating and antioxidation properties and is favorably utilized for machines and tools for food and agricultural products processing, like machines and tools, and items for food or agricultural products storage, preparation, cooking and handling.
2. Description of the Prior Art
For processing of agricultural products, livestock products, marine products and for preparation of food stuffs, various processes, such as selection, classification, grinding, mixing, baking, heating, fermentation, boiling, freeze drying and the like, are generally applied to the material and various kinds of food processing machines are utilized in these processes.
Examples of the machines for processing of agricultural products are machines and tools for collecting leaves from tea plants, rice cleaning machines, flour mills, brewing apparatus for production of sake, soy sauce, miso and the like and machines for the production of noodles, bread, cookies, fruit juice, jam, pickles and the like. Examples of machines for processing of livestock products are machines for processing milk, machines for production of milk products, such as cheese and butter, machines for processing meat and the like. Examples of machines for processing of marine products are machines for processing of fish meat, sea weeds and the like. Other examples of the food processing machines are apparatus for production of food additives, natural flavor and pharmaceutical products, such as a vacuum thin layer evaporator and a mixing apparatus.
For the purpose of lubrication of these food processing machines, oils of mineral origin, such as mineral oil and liquid paraffin, liquid vegetable oils, such as soy bean oil, cotton seed oil and rapeseed oil and animal oils and fats, such as beef tallow and lard are generally utilized. However, when oils of mineral origin are utilized, it is unavoidable that the oils are scattered or mixed into the foods or the agricultural products through rotating parts of the machines during long operation of the machines and the scattering and mixing of the oils of mineral origin into the foods and agricultural products are not desirable for food sanitation reasons. When liquid vegetable oils or animal oils and fats are utilized, oxidation stability is not sufficient even though they do not cause food sanitation problems.
The following oils and fats have been proposed as materials useful for food processing machines: (1) oil and fat utilized for spraying which comprises a transesterification product of 30 to 90 weight parts of oil and fat for foods containing less than 20 wt. % of saturated fatty acid and 70 to 10 weight parts of a composition containing a triglyceride of medium chain saturated fatty acids having 6 to 10 carbon atoms (MCT) as the main component (Laid Open Japanese Patent Publication Showa 56-72651); (2) a transesterification product of oil and fat made to contain increased amounts of monoene acids, such as oleic acid, and decreased amounts of polyene acids, such as linoleic acid and linolenic acid, by hydrogenation of vegetable oils, such as camellia oil, sasanqua oil, olive oil, safflower oil of high oleic acid content, hazelnut oil and rapeseed oil (Laid Open Japanese Patent Publications Showa 57-67695 and Showa 62-32841); (3) an oil of high oxidation stability and low cloud point which is prepared by transesterification of MCT and oil and fat of the vegetable oils described in (2) or hydrogenation products of oil and fats of the vegetable oils described in (2) (Laid Open Japanese Patent Publication Showa 61-173743).
However, the oils and fats of (1) through (3) contain large amounts of unsaturated acids such as oleic acid because they utilize soy bean oil, cotton seed oil, rapeseed oil, corn oil or oils which were made to contain increased amounts of oleic acid by reducing the content of polyene acids by hydrogenation to enhance oxidation stability. These oils have insufficient oxidation stability.
Another material proposed is a lubricating oil composition for food processing machines prepared by compounding triglycerides having linear alkyl group of 5 to 21 carbon atoms as the essential component and fatty acids of 12 to 22 carbon atoms (Laid Open Japanese Patent Publication Heisei 2-209995). However, this composition is based on the low viscosity MCT and has a problem that adjustment of the viscosity of the composition to a desired value is not always easy.
When vegetable oils are utilized as lubricating oils for food processing machines, they have problems that degradation of the oils takes place or seizure of machines takes place by hardening of the oils by polymerization because of unsaturated bonds in fatty acid molecules. The rate of oxidation of unsaturated fatty acids is larger than the rate of oxidation of saturated fatty acids. For example, the rates of oxidation of linoleic acid and linolenic acid at 20.degree. C. are 12 to 20 times and 25 times, respectively, larger than the rate of oxidation of oleic acid. Esters of saturated fatty acids are stable against oxidation. For example, the rate of oxidation of methyl stearate at 100.degree. C. is 1/11 and 1/100 of methyl oleate and methyl linoleate, respectively.
Oxidation stability and cloud point are, in general, related therefor each other. Oils and fats which contain larger amounts of unsaturated acids having higher oxygen absorption, such as oleic acid, linoleic acid and linolenic acid, in glyceride have lower oxidation stability and also a lower value of cloud point. Cloud point, pour point and solidifying point are also, in general, related therefore each other and a material having a higher cloud point has a higher pour point and a higher solidifying point. The properties of a material can be compared by utilizing either one of cloud point, pour point and solidifying point. An oil which is prepared by transesterification of MCT and an oil containing a large amount of oleic acid in which the contents of linoleic acid and linolenic acid are reduced by hydrogenation to enhance oxidation stability has a lower cloud point but is not sufficient in oxidation stability because oleic acid is also an unsaturated fatty acid.
Oils and fats containing larger amounts of saturated fatty acids having lower oxygen absorption, such as myristic acid, palmitic acid, stearic acid and the like, in glyceride have higher oxidation stability but higher cloud point at the same time.
Because lubricating oils are utilized for driving parts of various machines and tools, oils having viscosities suitable for each of the machines and tools are required. MCT which is considered to be the best material for the lubricating oil for food processing machines has satisfactory quality concerning high oxidation stability and low cloud point. However, MCT has too low viscosity when it is utilized without other components because the viscosity is 15 to 20 centipoises at 25.degree. C. and 10 to 15 centipoises at 40.degree. C.